This invention relates to vibration damping in hot gas turbine engines and other such rotary machines, and more particularly to improved hydraulic or viscous damping means associated with the bearing supports for rotating masses in such machines.
The occurrence of cyclical orbital motion of the shaft of a hot gas turbine engine rotor as a result of dynamic instability and rotor unbalance is well known, and fluid damping means such as squeeze film dampers are utilized to dampen orbital and other undesirable shaft motion. In general, such dampers include the use of a pressurized fluid, such as an oil, in a small damper space between a bearing support element, such as the outer circumferential surface of a rolling element bearing outer race, and an opposing annular wall of an annular bearing housing chamber in which the race is confined with permitted limited radial motion. Damper fluid is introduced into the defined annular damper space between the circumferential outer race and the annular housing, and vibratory or orbital motion of the bearing race causes the race to exert a squeezing action on the damper fluid to move or distribute the fluid throughout the defined damper space. Various sealing arrangements are employed to retain or seal the fluid in the damper space. In one such sealing arrangement, spaced apart opposite piston type rings are often employed between the bearing race and the housing as axial fluid seals for the damper space. A continuous supply of damper fluid is required for operation of such dampers, and optimum operation requires that the fluid be introduced in a timely and effective manner at a proper location in the damper. Accordingly, damper fluid supply and control, as well as effective operation of the piston ring seals, are important factors in squeeze film dampers and their operation.